Must sustaining a Ben Noach depend on formal acceptance of the Seven Mitzvot before a beit din, or is voluntary acceptance enough?

In a letter to the Rebbe, the Rogatchover seems to contradict his opinion as stated in the sicha. This shiur shows how a subtle remark in Shulei HaGilyon may resolve the apparent contradiction by distinguishing two forms of sustaining a Ben Noach.

לקוטי שיחות, חלק כו, יתרו ג